The US military created a detailed intelligence file on a London-based al-Qaida cell that did not exist, as a result of its reliance on tip-offs from one of its detainees, the Guantánamo files reveal.

One of the men whom the camp authorities believed to have been a leading member of the "cell" in the 1990s was 11 years old at the time, and had not left his family's village in Saudi Arabia.

The files on most of the other supposed members suggest that they, too, had never visited Britain.

A list of the members of the group described as the "London, United Kingdom-based al-Qaida cell" is to be found in the file of Yousef Abkir Salih al-Qarani.

This file wrongly states that he was born in Saudi Arabia in 1981. Lawyers representing him discovered that his birth certificate shows him to have been born in 1987.

The man who identified al-Qarani as having been a member of the London cell in 1998 was Mohammed Basardah, who has implicated at least 122 other inmates.

Basardah told the authorities that he had learned which prisoners were members of the "London cell" during conversations with Shaker Aamer, a former London resident who is still incarcerated in Guantánamo.

Basardah said he had learned that the leader of the cell was Abu Qatada, who was a well-known radical cleric in the city before 9/11.

Qatada's "second-in-command" was said to be Abu Hamza, another well-known figure.

The Guantánamo files show that the camp authorities accepted that the other members of the cell were a group of Saudi and Kuwaiti detainees. However, the files on these individuals, which detail their movements over many years, show no sign that they had ever visited Britain.